This invention relates generally to steam reformation of hydrocarbon, and more particularly to process and apparatus employing a porous ceramic reactor tube or tubes to achieve economic advantages.
The commercial application of steam reforming of hydrocarbons for the production of hydrogen, ammonia, methanol, and other products involves the catalytic reaction of a hydrocarbon feedstock with steam to form a mixture of hydrogen, carbon monoxide, carbon dioxide, water vapor, and residual hydrocarbons.
The reaction between methane and steam to produce hydrogen as well as carbon monoxide and carbon dioxide is a well-known chemical process which proceeds in accordance with the following chemical equations: EQU CH.sub.4 +H.sub.2 O.fwdarw.CO+3H.sub.2 ( 1) EQU CH.sub.4 +2H.sub.2 O.fwdarw.CO.sub.2 +4H.sub.2 ( 2)
The water gas shift reaction is also involved as follows: EQU CO+H.sub.2 O.fwdarw.CO.sub.2 +H.sub.2 ( 3)
All of the foregoing reactions are favored by the presence of appropriate catalytic materials. In the case of equations (1) and (2), the normal catalyst is nickel deposited on alumina support materials.
Reactions (1) and (2) are endothermic and require the rapid input of heat at high temperatures to cause the reaction to take place at an economic rate. Typically, the steam methane reformer is a furnace with multiple high temperature alloy tubes filled with nickel-impregnated carrier material, pelleted catalyst. Temperatures in the range of 700.degree. to 880.degree. C. are required to cause the system to reach equilibrium conversion levels for methane in the range of 90+ %. Some data giving typical equilibrium compositions of reformed methane as a function of the temperature are given in:
TABLE 1 ______________________________________ NORMAL EQUILIBRIUM COMPOSITION FOR METHANE STEAM REFORMING LOWER TEMPERATURE RANGE VOLUME % Temperature .degree.C. Component 350 403 463 524 584 664 ______________________________________ CH.sub.4 16.9 16.1 14.7 12.8 10.4 6.7 CO.sub.2 0.9 1.5 2.5 3.7 5.1 6.3 CO -- -- -- 0.1 0.6 2.1 H.sub.2 3.6 6.1 10.2 15.7 22.2 31.6 H.sub.2 O 78.5 76.3 72.6 67.7 61.7 53.3 ______________________________________
Catalytic steam reformer furnaces are conventially generally were limited to pressures less than about 500 psi at design temperatures of about 1,750.degree. F. (935.degree. C.), and with a mechanical limitation of about one-inch thickness for cast, high alloy steel tubes. Such tubes were required to be long, i.e., about ten meters, in commercial installation. There is need for an improved process and apparatus, and particularly a process making it possible to operate at lower temperatures and possibly pressure, enabling "once through" operation for high pressure hydrogen requirements as in methanol and ammonia plants, as well as hydrocracking.